ABSTRACT End stage renal disease (ESRD) requiring hemodialysis (HD) affects >400,000 patients in the US and is associated with high morbidity, mortality, and costs. While HD can prevent immediate death due to uremia, the long-term survival of patients on HD remains poor. Median survival from the time of initiating HD is 3 years and 5-year survival is <35%. Over 50% of all deaths in HD patients are due to cardiovascular disease (CVD) and 50% of these (25% of all deaths) are sudden cardiac deaths (SCD). The high rates of SCD in HD patients have not changed in recent decades. The key barrier to progress in reducing SCD rates in HD patients is our limited understanding of the mechanisms underlying SCD. It has been assumed that the arrhythmic mechanisms for SCD in HD were the same as in the general population and that the majority of cases were due to ventricular tachycardia / ventricular fibrillation (VT/VF), but other mechanisms have also been described in HD including bradyarrhythmias, asystole and non-arrhythmic events. Little is known regarding the prevalence of these mechanisms in HD and this is widely recognized as a major clinical challenge. In addition, several characteristics of the HD session may contribute to arrhythmic risk. The typical dialysate prescription, low in potassium and calcium and high in bicarbonate concentrations, and rapid fluid shifts and hypotension during HD may further increase the risk of arrhythmias. Previous studies of arrhythmic risk in HD patients have been limited by the lack of continuous cardiac monitoring or by small sample sizes. We propose to conduct the Cardiac Arrhythmia Monitoring and Related Outcomes in HD (CAMARO- HD) Study, a cohort study of the risk of developing cardiac arrhythmias and their associated outcomes among 1,000 patients recruited within the first 6 months of initiating HD. We will implant a subcutaneous cardiac monitor (Reveal LINQ) in each patient to continuously record the cardiac rhythm and identify all episodes of VT/VF, bradycardia, asystole, and atrial fibrillation during 3 years of follow-up. We will then evaluate the association of arrhythmic events and arrhythmic burden with study outcomes (all-cause mortality and heart failure hospitalization). CAMARO-HD will also test the hypothesis that specific characteristics of the HD session contribute to arrhythmic risk and will assess if differences in arrhythmic burden between Black and White patients mediate the well-known race-survival paradox in HD. CAMARO-HD will be the largest cohort of HD patients with long-term continuous cardiac monitoring and precise information on ventricular and atrial arrhythmic episodes with a sample size large enough to quantify their clinical consequences in terms of mortality and heart failure hospitalization. CAMARO-HD will also provide actionable information related to the arrhythmic mechanisms responsible for deaths or heart failure hospitalizations and to the association of specific characteristics of the HD session with arrhythmic events. This information will directly modify clinical practice and will inform the design of preventive trials.